3D Gamestudio Programmer's Manual © Conitec May 2001 1

3D GameStudio

Programmer's Manual

for A5 engine 5.10

Johann C. Lotter / Conitec May 2001 3D Gamestudio Programmer's Manual © Conitec May 2001 2

This manual is protected under the copyright laws of Germany and the U.S. Acknex and 3D GameStudio are trademarks of Conitec Corporation. Windows, DirectX and Direct3D are trademarks of Microsoft, Inc. Voodoo is a trademark of 3dfx, Inc. Quake is a trademark of Id Software, Inc. Any reproduction of the material and artwork printed herein without the written permission of Conitec is prohibited. We undertake no guarantee for the accuracy of this manual. Conitec reserves the right to make alterations or updates without further announcement. 3D Gamestudio Programmer's Manual © Conitec May 2001 3

Contents

The A5 DLL interface...... 4 Getting started with the SDK...... 4 Implementing new WDL functions...... 5 Writing to the screen buffer...... 5 Using Direct3D functions...... 5 Programming a game in VC++...... 6 WDL object structures...... 7 DLL interface structures...... 9 DLL functions...... 10 The A5 Client/Server Protocol...... 12 Client Messages...... 12 Server Messages...... 12 The MDL model format...... 14 MDL file header...... 14 MDL skin format...... 14 MDL skin vertices...... 15 MDL mesh triangles...... 15 MDL frames...... 16 MDL bones...... 17 3D Gamestudio Programmer's Manual © Conitec May 2001 4

The A5 DLL interface

DLLs can be used as extensions to the engine and to the WDL language, as well as for programming a game in VC++ instead of WDL. The DLL interface is available on all A5 editions. For creating an A5 DLL, the SDK (source development kit) and its DLL interface library is required. SDK owners can create arbitrary DLLs for adding new effects, actor AI or WDL instructions, and distribute or sell them to other 3D GameStudio users.

The Microsoft Visual C++ 6.0 development system is used for creating DLL extensions. The DLL SDK contains an interface library that must be linked to any DLL. An example VC++ project with a DLL template is also provided, which makes it easy to create extensions even for not-so-experienced C programmers who have never used DLLs before.

DLL extensions work bidirectionally: WDL instructions can access DLL functions, and DLL functions can access essential engine functions and variables. On opening a DLL, the engine transfers the pointer to an internal interface structure to the interface library. The interface contains pointers to engine variables and functions, like the frame buffer, the DirectX interface, the network interface, the DirectInput interface, the level, the WDL functions and so on. Theoretically everything - MP3 or MOD players, a physics engine, another 3D engine or even another scripting language - could be added to the engine this way.

On accessing system resources like sound, video, joystick and so on, the DLL must take care of possible resource conflicts. The engine shares its resources and expects the same from the code inside the DLL. For instance, code that requires exclusive access to the sound device (like some old MOD players) won't work. Some resources (like the midi player) can't be shared - if midi music is played by the DLL, the engine must not play a midi file at the same time and vice versa. Also care must be taken that for writing something into the frame buffer it must be locked before, and unlocked afterwards. The interface library provides functions for that.

Getting started with the SDK

The SDK comes with a DLL ackdll.dll that contains just a few typical example functions. For testing one of those DLL functions, just copy the compiled ackdll.dll into the work folder, and insert the following WDL instructions into a function assigned to a key:

dll_open("ackdll.dll"); dll_exec("PaintScreenWhite",0); // or any other DLL function dll_close(dll_handle);

For creating a new DLL, just unzip the SDK into any directory and open it as a VC++ 6.0 project. The source code of ackdll.dll is included. It contains typical examples for all sorts of DLL functions. In the following, some typical DLL uses are described.

All exported DLL functions must be of type DLLFUNC fixed func(long) or DLLFUNC fixed func(fixed), while fixed is a long integer interpreted by WDL as 22.10 fixed point value. The engine structs and functions accessible from DLL functions are described at the end of this chapers. All DLL functions can be accessed from WDL script through the dll_open, dll_close, dll_exec, and dll_exec_vec instructions that are described in the WDL manual. 3D Gamestudio Programmer's Manual © Conitec May 2001 5

Implementing new WDL functions

A DLL can contain a library of new arithmetic or other functions that can be accessed by WDL. The following example implements an exp function (which is already available in WDL) just for demonstration purpose:

// returns e power n DLLFUNC fixed Exp(fixed var) { return (FLOAT2FIX(exp(FIX2FLOAT(var)))); }

After having openend the DLL, the new function can be used this way: x = dll_exec("Exp",y); // calculates x = e power y

Writing to the screen buffer

The following simple example shows how to lock the screen buffer, write into it and unlock it again. It paints the screen all white for one frame. This works in D3D as well as in 8-bit mode. From WDL, activate this function through dll_exec("PaintScreenWhite",0).You'llseeashort white flash when you call this function once. If you call it in a wait(1)-loop, the screen will become all white.

DLLFUNC fixed PaintScreenWhite (long unused) { // retrieve the pointer to the screen buffer FRAME_INTERFACE *a5fb = a5->fb;

// lock the screen buffer to get access to it (*a5fb->Lock)();

// paint it all white; note the use of a5fb->pitch here for (int j=0; jheight; j++) { byte *buffer = a5fb->bytes + j*a5fb->pitch; for (int i=0; iwidth*a5fb->bpp; i++) *buffer++ = 255; }

// unlock it so that A5 can use it again (*a5fb->Unlock)();

return 0; }

Using Direct3D functions

The following example shows how easy it is to use Direct3D functions for creating some effects on the screen. As all initialization is done by the engine, it is sufficient just to call the draw functions. All Direct3D functions are accessed through a IDirect3DDevice7 pointer that is available through the DLL. For details refer to the DirectX documentation that is available, along with the DirectX 7 SDK, from the Microsoft site. 3D Gamestudio Programmer's Manual © Conitec May 2001 6

The example paints a multicolored triangle onto the screen. From WDL, activate this function through dll_exec("PaintD3DTriangle",0).You'll see the triangle briefly flashing in the upper left corner when you call this function once. If you call it in a wait(1)-loop, the triangle will be permanently on the screen. This code only works in 16- or 32-bit mode when Direct3D is activated.

#include // from the DIRECTX7 sdk

DLLFUNC fixed PaintD3DTriangle (long unused) { // get the active D3D device FRAME_INTERFACE *a5fb = a5->fb; IDirect3DDevice7 *pd3ddev = (IDirect3DDevice7 *) a5fb->pd3ddev; if (!pd3ddev) return 0; // no D3D device in 8 bit mode

// define three corner vertices D3DTLVERTEX v[3];

v[0].sx = 10.0; v[0].sy = 10.0; v[0].color = 0xFFFF0000; // the red corner v[1].sx = 310.0; v[1].sy = 10.0; v[1].color = 0xFF0000FF; // the blue corner v[2].sx = 10.0; v[2].sy = 310.0; v[2].color = 0xFF00FF00; // the green corner

v[0].sz = v[1].sz = v[2].sz = 0.0; // z buffer - paint over everything v[0].rhw = v[1].rhw = v[2].rhw = 1.0; // no perspective

// begin a scene - needed before D3D draw operations pd3ddev->BeginScene();

// set some render and stage states (you have to set some more for more complicated operations) pd3ddev->SetRenderState(D3DRENDERSTATE_ALPHABLENDENABLE,FALSE); pd3ddev->SetTextureStageState(0,D3DTSS_COLORARG2,D3DTA_DIFFUSE); pd3ddev->SetTextureStageState(0,D3DTSS_COLOROP,D3DTOP_SELECTARG2);

// now draw the triangle pd3ddev->DrawPrimitive(D3DPT_TRIANGLEFAN,D3DFVF_TLVERTEX,(LPVOID)v,3,0);

// Normally we have to store the old render and texture states before, and // set them back here... but the simple states above do no harm

// do not forget to do a clean close of the scene pd3ddev->EndScene(); return 0; }

Programming a game in VC++

Using the A4_ENTITY object (see below), a DLL can implement complex AI functions that would be harder to code in WDL. Even the whole gameplay could be written in a DLL. The following example shows how to change entity parameters through a DLL function.

// rolls the given entity by 180 degrees DLLFUNC fixed FlipUpsideDown(long entity) { if (!entity) return 0;

// retrieve the pointer to the given entity A4_ENTITY *ent = (A4_ENTITY *)entity;

// set the entity's roll angle to 180 degrees ent->roll = FLOAT2FIX(180);

return 0; 3D Gamestudio Programmer's Manual © Conitec May 2001 7

}

This would be called by WDL through dll_exec("FlipUpsideDown",my). For controlling entities totally through a DLL – for instance, when you intend to write your whole game in VC++ instead of WDL – WDL dummy actions can be assigned to the entity, like this: var appdll_handle; function main() { // open the application DLL appdll_handle = dll_open("myapp.dll"); ... } action myent_event { dll_handle = appdll_handle; dll_exec("myent_event",my); // this DLL function handles all entity events } action myentity { my.event = myent_event; while(1) { dll_handle = appdll_handle; dll_exec("myent_main",my); // this DLL function controls the entity wait(1); } }

WDL object structures

Pointers to WDL objects can be transferred to DLL functions, thus allowing object manipulation. The internal engine format of some important WDL objects is listed here (the structs are defined in the a5dll.h file).

#define DLLFUNC extern "C" __declspec(dllexport) typedef unsigned char byte; typedef long fixed; // fixed point 22.10 number format used by WDL #define INT2FIX(i) ((i)<<10) #define FIX2INT(x) ((x)>>10) #define FIX2FLOAT(x) (((double)(x))/(1<<10)) #define FLOAT2FIX(f) ((fixed)((f)*(1<<10)))

/////////////////////////////////////////////////////////////////////// // internal A4 / A5 structs typedef struct { long index; // internal use only long next; // internal use only char *name; // pointer to WDL name of the object } WDL_LINK; // WDL object header typedef struct { WDL_LINK link; long modelkey; // internal use only fixed x,y,z; // position of the entity fixed pan,tilt,roll; // euler angles fixed scale_x,scale_y,scale_z; // scale factors, 0..255 long flags; // entity property flags, see ENF... union { fixed frame; // frame number for sprites & models 3D Gamestudio Programmer's Manual © Conitec May 2001 8

fixed u; // texture x offset for maps }; union { fixed nextframe; // interpolation target frame for models fixed v; // texture y offset for maps }; fixed skin; // skin texture number for models fixed ambient; // -100..+100 fixed albedo; // 0..100, light reflectivity fixed alpha; // 0..100, transparency, default 50 fixed lightrange; // dynamic light range in quants fixed red,green,blue; // dynamic light color, 0..255 long emask; // event enable flags, EVF... long eflags; // internal status flags fixed min[3],max[3]; // bounding box in quants fixed trigger_range; fixed push; fixed shadow_range; fixed floor_range; long client_id; // client # that has created this entity fixed skill[48]; // entity skills } A4_ENTITY; typedef struct { WDL_LINK link; char *text; // pointer to null terminated string long length; // allocated length of string (NEVER exceed!) long flags; // 0 = don't save, 1 = save string at SAVE/LOAD } A4_STRING; typedef struct { void *pd3dsurf; // pointer to the DirectDrawSurface7 (unlock before writing to it) long finalwidth,finalheight; // allocated size of the d3dsurf (not necessary the size of the bitmap!) byte *pixels; // pointer to the original pixels byte *palette; // pointer to the original palette when 8 bit long bitspp; // original bitspp - 8, 16, 24, or 32 long width,height; // original size of the bitmap long pitch; // original size of a horizontal line long flags; } A4_TEX; typedef struct { WDL_LINK link; long width,height; // size of the bitmap long bpp; // internal bytes per pixel (1 or 2) long flags; // 0 = don't save, 1 = save images at SAVE/LOAD byte *pixels8; // pointer to 8 bit image (color indexes) byte *pixels16; // NULL when palettized, otherwise ptr to 5-6-5 or 4-4-4-4 coded 16-bit image A4_TEX *tex; // pointer to one or more textures the image is split into } A4_BMAP; typedef struct { WDL_LINK link; long type; // internal use only fixed layer; // layer number (read only) fixed pos_x,pos_y; // screen position in pixels long flags; fixed alpha; // transparency factor fixed offset; // vertical offset fixed lines; // number of lines to display long fontkey; // internal use only long strings; // number of strings (read only) A4_STRING **pstrings; // pointer to array of string pointers } A4_TEXT; typedef struct { WDL_LINK link; long type; // internal use only fixed layer; // layer number (read only) 3D Gamestudio Programmer's Manual © Conitec May 2001 9

fixed pos_x,pos_y; // screen position in pixels long flags; fixed alpha; // transparency factor A4_BMAP *bmap; // background bitmap } A4_PANEL; typedef struct { WDL_LINK link; long type; // internal use only fixed layer; // layer number (read only) fixed pos_x,pos_y; // screen position in pixels long flags; fixed size_x,size_y; // screen size in pixels fixed x,y,z; // position of the camera fixed pan,tilt,roll; // camera angles fixed offset_x,offset_y; // eye offsets fixed arc; // camera FOV, used for zooming fixed aspect; // width to height ratio fixed ambient; // brightness fixed fog; // fog strength fixed diameter; // camera size for collision detection A4_ENTITY *genius;// gives valid BSP tree leaf for the view } A4_VIEW;

DLL interface structures

Internal structs are handed over to the DLL for accessing internal variables and pointers initialized by the engine. typedef struct { byte *bytes; // pointer to frame buffer (only valid after Lock) int pitch; // size of a horizontal line in bytes (!= width!) int width,height; // width, height of the screen int bpp; // bytes per pixel of the frame buffer

BOOL (*Lock)(void); // lock frame buffer before accessing it void (*Unlock)(void); // unlock frame buffer after accessing it void *pd3ddev; // pointer to the IDirect3DDevice7 initilized by A4/A5 } FRAME_INTERFACE; typedef struct { void *pdi; // pointer to the IDirect3DDevice7 used by A4/A5 void *pdimouse; // pointer to the mouse DirectInputDevice void *pdikbd; // always zero (keyboard doesn't use DirectInput) void *pdijoy; // always zero (joystick doesn't use DirectInput) void *pdplay; // pointer to the DirectPlay4 interface void *pdplobby; // pointer to the DirectPlayLobby2A interface DWORD pdplayer; // player ID void *pdpguid; // multiplayer session GUID void *pds; // pointer to the DirectSound interface void *pdsb; // pointer to the DirectSoundBuffer interface } DX_INTERFACE; typedef struct { long (*GetObj)(char *name); // internal use only long (*GetFunc)(char *name);// internal use only A4_ENTITY **my,**you; // Pointer to MY, YOU entity pointers } WDL_INTERFACE;

typedef struct { long dll_version; // The version is automatically tested against A5DLL_VERSION // on opening the DLL. DLLs work with engines with the same or a higher // version number, but not with a lower version engine. 3D Gamestudio Programmer's Manual © Conitec May 2001 10

WDL_INTERFACE *wdl; // access to MY and YOU pointers FRAME_INTERFACE *fb; // access to the frame buffer and the Direct3D Device DX_INTERFACE *dx; // access to directx pointers } A5_INTERFACE;

An A5_INTERFACE object named a5 is initialized on startup of each DLL and can be used for accessing the screen buffer, the Direct3D Device and the MY and YOU entities. For directly accessing any WDL object from a DLL, the a5dll.lib canbeusedinawaydescribedinthe following chapter.

DLL functions

Two functions in the a5dll.lib provide DLL access to internal WDL variables, objects and WDL script functions. This way, entity AI can be implemented in a DLL plugin, and can use most WDL script instructions. long a5dll_getwdlobj(char *name);

This function returns the address of the WDL object or variable with the given name. It can be used to read or write any defined WDL object from inside a DLL plugin. If the object does not exist, NULL is returned and an error message will pop up. Examples for DLL functions that access WDL objects:

// adds the given value to the sky speed fixed AddToSkySpeed(fixed value) { // get the address of the variable fixed *skyspeed = (fixed *)a5dll_getwdlobj("sky_speed"); if (!skyspeed) return 0;

// add the value to both the x and y components skyspeed[0] += value; // skyspeed X value skyspeed[1] += value; // skyspeed y value

return INT2FIX(1); }

// zooms the camera view fixed ZoomIn(fixed value) { A4_VIEW *camera = (A4_VIEW *)a5dll_getwdlobj("camera"); if (!camera) return 0; return (camera->arc -= value); // change the FOV and return it } long a5dll_getwdlfunc(char *name);

This function returns the address of the WDL function with the given name. It can be used to execute WDL functions from inside a DLL plugin. Not all WDL functions are available for DLLs. If the function is not available (as can be the case for some special WDL functions, like wait() or inkey()), NULL is returned and an error message will pop up. Example for an entity AI DLL function that uses WDL functions for scanning the environment of an entity:

// returns free distance in front of MY entity until next obstacle fixed DistAhead(long my) { if (!my) return 0; 3D Gamestudio Programmer's Manual © Conitec May 2001 11

// retrieve the pointer to the given entity A4_ENTITY *ent = (A4_ENTITY *)my;

// get the address of some wdl variables and functions fixed *tracemode = (fixed *)a5dll_getwdlobj("trace_mode"); wdlfunc2 vecrotate = (wdlfunc2)a5dll_getwdlfunc("vec_rotate"); wdlfunc2 trace = (wdlfunc2)a5dll_getwdlfunc("trace"); if (!tracemode || !trace || !vecrotate) return 0;

fixed target[3] = { FLOAT2FIX(1000.0),0,0 }; // trace target vector

// rotate vector by entity engles, just as in WDL (*vecrotate)((long)target,(long)&(ent->pan));

// add entity position to target target[0] += ent->x; target[1] += ent->y; target[2] += ent->z;

// set trace_mode, then trace a line between entity and target, // and return the result *tracemode = INT2FIX(TRM_IGNORE_ME + TRM_IGNORE_PASSABLE + TRM_USE_BOX); return (*trace)((long)&(ent->x),(long)target); }

Global WDL functions, like level loading and keyboard entry, can not be called directly from a DLL. However they can be executed indirectly from a WDL script that calls a DLL function for deciding which operation must be executed. Example: function main_loop { while(1) { dll_handle = appdll_handle; operation = dll_exec("choose_operation",0); // this function returns a control code if (operation == 1) { load_level(); } if (operation == 2) { load_level(); } if (operation == 10) { inkey(entry_string); } wait(1); } } 3D Gamestudio Programmer's Manual © Conitec May 2001 12

The A5 Client/Server Protocol

The structure of the messages is a single-byte code, followed by code-dependant informations. When describing the content of messages, we will use the following conventions: String = a sequence of characters, terminated by NULL ('\0') Angle = a short, to be multiplied by 360.0/65535.0 to convert it to degrees. Position – a position packed in three bytes by dividing it by 8. Byte = an unsigned integer, on one byte. Scale(x) = a value packed into one byte to be multiplied by x/255.0. Short = a signed integer, on two bytes, Big Endian order (Intel order). Long = a signed integer, on four bytes, Big Endian order (Intel order). Fixed = a floating point number, on four bytes, Big Endian order (Intel order).

Client Messages

The following commands are used for transferring information from the client to the server:

Command Bytecode Arguments Description CLS_JOIN 0x02 Request for joining the session CLS_CREATE 0x03 Create entity with given model name, and link client to it CLS_REMOVE 0x04 Remove entity on server CLS_PING 0x07 Sent after each client frame CLS_LEAVE 0x08 Leave the session CLS_LEVEL 0x09 Client has loaded a level CLS_VAR 0x0a Send a variable CLS_STRING 0x0b Send a string CLS_SKILL 0x0e Send an entity skill CLS_SKILL3 0x0f Send an entity vector skill

Server Messages

The following commands are used for transferring information from the server to either a specific client, or to all clients connected:

Command Bytecode Arguments Description SVC_CREATE 0x03 Created entity with given index SVC_REMOVE 0x04 Removed entity from server SVC_ENTSOUND 0x05 Play an entity sound on the clients SVC_PARTICLE 0x06 Generate a particle effect on the clients SVC_INFO 0x07 Send the server time to the clients SVC_LEAVE 0x08 Server goes down 3D Gamestudio Programmer's Manual © Conitec May 2001 13

Command Bytecode Arguments Description SVC_VAR 0x0a Send a variable to all clients CLS_STRING 0x0b Send a string to all clients SVC_SKILL 0x0e Send an entity skill to the entity's client SVC_SKILL3 0x0f Send an entity vector skill to the entity's client SVC_UPDATE1 0x40 Update entity parameters 1 SVC_UPDATE2 0x80 Update entity parameters 2 SVC_UPDATE3 0xc0 Update entity parameters 3 3D Gamestudio Programmer's Manual © Conitec May 2001 14

The MDL model format

A wireframe mesh, made of triangles, gives the general shape of a model. 3D vertices define the position of triangles. For each triangle in the wireframe, there will be a corresponding triangle cut from the skin picture. Or, in other words, for each 3D vertex of a triangle that describes a XYZ position, there will be a corresponding 2D vertex positioned that describes a UV position on the skin picture.

It is not necessary that the triangle in 3D space and the triangle on the skin have the same shape (in fact, it is not possible for all triangles), but they should have shapes roughly similar, to limit distortion and aliasing. Several animation frames of a model are just several sets of 3D vertex positions. The 2D vertex positions always remain the same.

A MDL file contains: - A list of skin textures in 8-bit palettized, 16-bit 565 RGB or 16 bit 4444 ARGB format. - A list of skin vertices, that are just the UV position of vertices on the skin texture. - A list of triangles, which describe the general shape of the model. - A list of animation frames. Each frame holds a list of 3D vertices. - A list of bone vertices, which are used for creating the animation frames.

MDL file header

Once the file header is read, all the other model parts can be found just by calculating their position in the file. Here is the format of the .MDL file header: typedef float vec3[3]; typedef struct { char version[4]; // "MDL3" or "MDL4" long final; // not used yet vec3 scale; // 3D position scale factors. vec3 offset; // 3D position offset. float pad; // not used yet. vec3 eye; // not used yet. long numskins ; // number of skin textures long skinwidth; // width of skin texture; must be a multiple of 2 long skinheight; // height of skin texture long numverts; // number of 3d wireframe vertices long numtris; // number of triangles surfaces long numframes; // number of frames long numskinverts; // number of 2D skin vertice long flags; // 0 = normal, 1 = terrain model long numbones; // number of bone vertices (MDL4 only, otherwise 0) } mdl_header;

The size of this header is 0x54 bytes (84).

The "MDL3" format is used by the A4 engine, while the "MDL4" format is used by the A5 engine. After the file header follow the skins, the skin vertices, the triangles, the frames, and finally the bones (future expansion).

MDL skin format

The model skins are flat pictures that represent the texture that should be applied on the model. There can be more than one skin. You will find the first skin just after the model header, at offset baseskin = 0x54. There are numskins skins to read. Each of these model skins is either in 8-bit palettized (type == 0), in 16-bit 565 format (type == 2) or 16-bit 4444 format (type == 3). The structure is: 3D Gamestudio Programmer's Manual © Conitec May 2001 15

typedef byte unsigned char; typedef struct { int skintype; // 0 for 8 bit (bpp == 1), 2 for 565 RGB, 3 for 4444 ARGB (bpp == 2) byte skin[skinwidth*skinheight*bpp]; // the skin picture } mdl_skin_t;

8 bit skins are a table of bytes, which represent an index in the level palette. If the model is rendered in overlay mode, index 0x00 indicates transparency. 16 bit skins are a table of shorts, which represent a true colour with the upper 5 bits for the red, the middle 6 bits for the green, and the lower 5 bits for the blue component. Green has one bit more because the human eye is more sensitive to green than to other colours. If the model is rendered in overlay mode, colour value 0x0000 indicates transparency. 16 bit alpha channel skins are represented as a table of shorts with 4 bits for each of the alpha, red, green, and blue component.

The width of skins should be a multiple of 4, to ensure long word alignement. The skin pictures are usually made of as many pieces as there are independent parts in the model. For instance, for the a player, there may be two pieces that defines the body, and two others that define the gun.

MDL skin vertices

The list of skin vertices indicates only the position on texture picture, not the 3D position. That's because for a given vertex, the position on skin is constant, while the position in 3D space varies with the animation. The list of skin vertices is made of these structures: typedef struct { short u; // position, horizontally in range 0..skinwidth-1 short v; // position, vertically in range 0..skinheight-1 } mdl_uvvert_t; mdl_uvvert_t skinverts[numskinverts]; u and v are the pixel position on the skin picture. The skin vertices are stored in a list, that is stored at offset basestverts = baseskin + skinsize. skinsize is the sum of the size of all skin pictures. If they are all 8-bit skins, then skinsize = (4 + skinwidth * skinheight) * numskins. If they are 16-bit skins, then skinsize = (4 + skinwidth * skinheight * 2) * numskins.

MDL mesh triangles

The model wireframe mesh is made of a set of triangle facets, with vertices at the boundaries. Triangles should all be valid triangles, not degenerates (like points or lines). The triangle face must be pointing to the outside of the model. Only vertex indexes are stored in triangles. Here is the structure of triangles: typedef struct { short index_xyz[3]; // Index of 3 3D vertices in range 0..numverts short index_uv[3]; // Index of 3 skin vertices in range 0..numskinverts } mdl_triangle_t; mdl_triangle_t triangles[numtris];

At offset basetri = baseverts + numskinverts * sizeof(uvvert_t) in the .MDL file you will find the triangle list. 3D Gamestudio Programmer's Manual © Conitec May 2001 16

MDL frames

A model contains a set of animation frames, which can be used in relation with the behavior of the modeled entity, so as to display it in various postures (walking, attacking, spreading its guts all over the place, etc). Basically the frame contains of vertex positions and normals. Because models can have ten thousands of vertices and hundreds of animation frames, vertex posistion are packed, and vertex normals are indicated by an index in a fixed table, to save disk and memory space.

Each frame vertex is defined by a 3D position and a normal for each of the 3D vertices in the model. In the MDL3 format, the vertices are always packed as bytes; in the MDL4 format that is used by the A5 engine they can also be packed as words (unsigned shorts). Therefore the MDL4 format allows more precise animation of huge models, and inbetweening with less distortion. typedef struct { byte rawposition[3]; // X,Y,Z coordinate, packed on 0..255 byte lightnormalindex; // index of the vertex normal } mdl_trivertxb_t; typedef struct { unsigned short rawposition[3]; // X,Y,Z coordinate, packed on 0..65536 byte lightnormalindex; // index of the vertex normal byte boneindex; // index of the bone this vertex belongs to } mdl_trivertxs_t;

To get the real X coordinate from the packed coordinates, multiply the X coordinate by the X scaling factor, and add the X offset. Both the scaling factor and the offset for all vertices can be found in the mdl_header struct. The formula for calculating the real vertex positions is: float position[i] = (scale[i] * rawposition[i] ) + offset[i];

The lightnormalindex field is an index to the actual vertex normal vector. This vector is the average of the normal vectors of all the faces that contain this vertex. The normal is necessary to calculate the Gouraud shading of the faces, but actually a crude estimation of the actual vertex normal is sufficient. That's why, to save space and to reduce the number of computations needed, it has been chosen to approximate each vertex normal. The ordinary values of lightnormalindex are comprised between 0 and 161, and directly map into the index of one of the 162 precalculated normal vectors: float lightnormals[162][3] = { {-0.525725, 0.000000, 0.850650}, {-0.442863, 0.238856, 0.864188}, {-0.295242, 0.000000, 0.955423}, {-0.309017, 0.500000, 0.809017}, {-0.162460, 0.262866, 0.951056}, {0.000000, 0.000000, 1.000000}, {0.000000, 0.850651, 0.525731}, {-0.147621, 0.716567, 0.681718}, {0.147621, 0.716567, 0.681718}, {0.000000, 0.525731, 0.850651}, {0.309017, 0.500000, 0.809017}, {0.525731, 0.000000, 0.850651}, {0.295242, 0.000000, 0.955423}, {0.442863, 0.238856, 0.864188}, {0.162460, 0.262866, 0.951056}, {-0.681718, 0.147621, 0.716567}, {-0.809017, 0.309017, 0.500000}, {-0.587785, 0.425325, 0.688191}, {-0.850651, 0.525731, 0.000000}, {-0.864188, 0.442863, 0.238856}, {-0.716567, 0.681718, 0.147621}, {-0.688191, 0.587785, 0.425325}, {-0.500000, 0.809017, 0.309017}, {-0.238856, 0.864188, 0.442863}, {-0.425325, 0.688191, 0.587785}, {-0.716567, 0.681718, -0.147621}, {-0.500000, 0.809017, -0.309017}, {-0.525731, 0.850651, 0.000000}, {0.000000, 0.850651, -0.525731}, {-0.238856, 0.864188, -0.442863}, {0.000000, 0.955423, -0.295242}, {-0.262866, 0.951056, -0.162460}, {0.000000, 1.000000, 0.000000}, {0.000000, 0.955423, 0.295242}, {-0.262866, 0.951056, 0.162460}, {0.238856, 0.864188, 0.442863}, {0.262866, 0.951056, 0.162460}, {0.500000, 0.809017, 0.309017}, {0.238856, 0.864188, -0.442863}, {0.262866, 0.951056, -0.162460}, {0.500000, 0.809017, -0.309017}, {0.850651, 0.525731, 0.000000}, {0.716567, 0.681718, 0.147621}, {0.716567, 0.681718, -0.147621}, {0.525731, 0.850651, 0.000000}, {0.425325, 0.688191, 0.587785}, {0.864188, 0.442863, 0.238856}, {0.688191, 0.587785, 0.425325}, {0.809017, 0.309017, 0.500000}, {0.681718, 0.147621, 0.716567}, {0.587785, 0.425325, 0.688191}, {0.955423, 0.295242, 0.000000}, {1.000000, 0.000000, 0.000000}, {0.951056, 0.162460, 0.262866}, {0.850651, -0.525731, 0.000000}, {0.955423, -0.295242, 0.000000}, {0.864188, -0.442863, 0.238856}, {0.951056, -0.162460, 0.262866}, {0.809017, -0.309017, 0.500000}, {0.681718, -0.147621, 0.716567}, {0.850651, 0.000000, 0.525731}, {0.864188, 0.442863, -0.238856}, {0.809017, 0.309017, -0.500000}, {0.951056, 0.162460, -0.262866}, {0.525731, 0.000000, -0.850651}, {0.681718, 0.147621, -0.716567}, 3D Gamestudio Programmer's Manual © Conitec May 2001 17

{0.681718, -0.147621, -0.716567}, {0.850651, 0.000000, -0.525731}, {0.809017, -0.309017, -0.500000}, {0.864188, -0.442863, -0.238856}, {0.951056, -0.162460, -0.262866}, {0.147621, 0.716567, -0.681718}, {0.309017, 0.500000, -0.809017}, {0.425325, 0.688191, -0.587785}, {0.442863, 0.238856, -0.864188}, {0.587785, 0.425325, -0.688191}, {0.688197, 0.587780, -0.425327}, {-0.147621, 0.716567, -0.681718}, {-0.309017, 0.500000, -0.809017}, {0.000000, 0.525731, -0.850651}, {-0.525731, 0.000000, -0.850651}, {-0.442863, 0.238856, -0.864188}, {-0.295242, 0.000000, -0.955423}, {-0.162460, 0.262866, -0.951056}, {0.000000, 0.000000, -1.000000}, {0.295242, 0.000000, -0.955423}, {0.162460, 0.262866, -0.951056}, {-0.442863,-0.238856, -0.864188}, {-0.309017,-0.500000, -0.809017}, {-0.162460, -0.262866, -0.951056}, {0.000000, -0.850651, -0.525731}, {-0.147621, -0.716567, -0.681718}, {0.147621, -0.716567, -0.681718}, {0.000000, -0.525731, -0.850651}, {0.309017, -0.500000, -0.809017}, {0.442863, -0.238856, -0.864188}, {0.162460, -0.262866, -0.951056}, {0.238856, -0.864188, -0.442863}, {0.500000, -0.809017, -0.309017}, {0.425325, -0.688191, -0.587785}, {0.716567, -0.681718, -0.147621}, {0.688191, -0.587785, -0.425325}, {0.587785, -0.425325, -0.688191}, {0.000000, -0.955423, -0.295242}, {0.000000, -1.000000, 0.000000}, {0.262866, -0.951056, -0.162460}, {0.000000, -0.850651, 0.525731}, {0.000000, -0.955423, 0.295242}, {0.238856, -0.864188, 0.442863}, {0.262866, -0.951056, 0.162460}, {0.500000, -0.809017, 0.309017}, {0.716567, -0.681718, 0.147621}, {0.525731, -0.850651, 0.000000}, {-0.238856, -0.864188, -0.442863}, {-0.500000, -0.809017, -0.309017}, {-0.262866, -0.951056, -0.162460}, {-0.850651, -0.525731, 0.000000}, {-0.716567, -0.681718, -0.147621}, {-0.716567, -0.681718, 0.147621}, {-0.525731, -0.850651, 0.000000}, {-0.500000, -0.809017, 0.309017}, {-0.238856, -0.864188, 0.442863}, {-0.262866, -0.951056, 0.162460}, {-0.864188, -0.442863, 0.238856}, {-0.809017, -0.309017, 0.500000}, {-0.688191, -0.587785, 0.425325}, {-0.681718, -0.147621, 0.716567}, {-0.442863, -0.238856, 0.864188}, {-0.587785, -0.425325, 0.688191}, {-0.309017, -0.500000, 0.809017}, {-0.147621, -0.716567, 0.681718}, {-0.425325, -0.688191, 0.587785}, {-0.162460, -0.262866, 0.951056}, {0.442863, -0.238856, 0.864188}, {0.162460, -0.262866, 0.951056}, {0.309017, -0.500000, 0.809017}, {0.147621, -0.716567, 0.681718}, {0.000000, -0.525731, 0.850651}, {0.425325, -0.688191, 0.587785}, {0.587785, -0.425325, 0.688191}, {0.688191, -0.587785, 0.425325}, {-0.955423, 0.295242, 0.000000}, {-0.951056, 0.162460, 0.262866}, {-1.000000, 0.000000, 0.000000}, {-0.850651, 0.000000, 0.525731}, {-0.955423, -0.295242, 0.000000}, {-0.951056, -0.162460, 0.262866}, {-0.864188, 0.442863, -0.238856}, {-0.951056, 0.162460, -0.262866}, {-0.809017, 0.309017, -0.500000}, {-0.864188,-0.442863, -0.238856}, {-0.951056,-0.162460, -0.262866}, {-0.809017, -0.309017, -0.500000}, {-0.681718, 0.147621, -0.716567}, {-0.681718, -0.147621, -0.716567}, {-0.850651, 0.000000, -0.525731}, {-0.688191, 0.587785, -0.425325}, {-0.587785, 0.425325, -0.688191}, {-0.425325, 0.688191, -0.587785}, {-0.425325,-0.688191, -0.587785}, {-0.587785,-0.425325, -0.688191}, {-0.688197,-0.587780, -0.425327} };

A whole frame has the following structure: typedef struct { long type; // 0 for byte-packed positions, and 2 for word-packed positions mdl_trivertx_t bboxmin,bboxmax; // bounding box of the frame char name[16]; // name of frame, used for animation mdl_trivertx_t vertex[numverts]; // array of vertices, either byte or short packed } mdl_frame_t;

The size of each frame is sizeframe = 20 + (numverts+2) * sizeof(mdl_trivertx_t), while mdl_trivertx_t is either mdl_trivertxb_t or mdl_trivertxs_t, depending on whether the type is 0 or 2. In the MDL3 format the type is always 0. The beginning of the frames can be found in the .MDL file at offset baseframes = basetri + numtris * sizeof(mdl_triangle_t).

MDL bones

This is only for future expansion of the MDL format, and not implemented yet.

Bones are a linked list of 3D vertices that are used for animation in the MDL4 format. Each bone vertex can have a parent, and several childs. If a bone vertex is moved, the childs move with it. If on moving a bone vertex the connection line to his parent rotates, it's childs are rotated likewise about the parent position. If the distance of the bone vertex to its parent changes, the change is added onto the distance between childs and parent. So the movement of the childs is done in a spherical coordinate system, it is a combination of a rotation and a radius change. Each bone vertex has an influence on one or more mesh vertices. The mesh vertices influenced by a bone vertex move the same way as it's childs. If a mesh vertex is influenced by several bone vertices, it is moved by the average of the bone's movement.